This study enrolls HBV mono-infected pregnant women cohorts managed in outpatient clinics/delivery unit at YouAn Hospital in Beijing. Subjects are prospectively followed from gestation week 26 to postpartum week 52. Treatment naïve mothers with HBV DNA > 6 log10 c/mL and normal ALT are eligible. Mothers with abnormal fetus, cirrhosis or evidence of hepatocellular carcinoma (HCC) are excluded. At gestation week 28, mothers will receive telbivudine (LdT) 600 mg per day or lamivudine (Lam) 100 mg per day until postpartum 4 or no treatment as per their preference. All infants will receive standard immunoprophylaxis. Data is collected from patient records using data extraction forms. Primary endpoints are vertical transmission rates at infants' age of 52 week and the safety of telbivudine or lamivudine use.